JP2000107570A - METHOD AND APPARATUS FOR REDUCING SOx AND NOx CONCENTRATION IN EXHAUST BOILER GAS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the SOx concn. together with the amt. of NH3 injected in a method for reducing SOx and NOx concns. in an exhaust gas produced by burning a fuel having high S and V contents in a boiler by injecting a gas for an ignition burner into the vicinity of an exhaust gas introduction port of a denitration apparatus at the downstream side of the boiler. SOLUTION: A fuel having high S and V contents, such as an olimulsion, is fed from burners 5 installed in a boiler 1 and is burned. Then, enough air is supplied from an over air port 6 installed at the downstream side of the burners 5 to conduct two-step burning to completely burn CO. An exhaust boiler gas is discharged through the top of the boiler 1, is caused to pass through a gas mixer to make the concn. distribution of each gas in the exhaust gas uniform, and is introduced into a denitration apparatus 2. An LPG gas, as a reducing component for the exhaust gas, is injected into the vicinity of the exhaust gas introduction port of the denitration apparatus 2 through an LPG gas supply device 8 and an LPG gas injection line 9. Thus, the amt. of NH3 injected into the exhaust gas is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the boiler relates to SO _X and NO _X concentration reduction method and apparatus in an exhaust gas, particularly, a high S, boiler exhaust gas at the time of a fuel containing V content is burned in a boiler And a method and apparatus for reducing SO _X and NO _X concentrations.

[0002]

2. Description of the Related Art In a general flue gas treatment system, boiler exhaust gas generated by boiler combustion is sequentially de-evaporated.
NO _X (denitrator), AH (air heater), EP (electrostatic precipitator), GGH (gas-gas heaters), is guided to the desulfurization apparatus. Here, in the De-NO _X, to remove the NO _X in the boiler in the exhaust gas, the SO _X removed in the desulfurization apparatus, and discharged to the atmosphere through the chimney after the clean gas.

[0003] When orimulsion containing high S and V components is used as boiler fuel, exhaust gas containing high concentrations of SO _X and NO _X is discharged from the boiler during boiler combustion. Here, the SO contained in the exhaust gas of the flue gas treatment system
_{Of the X} (SO ₂ , SO _3, etc.), SO ₃ has a strong corrosive property when it is sulfated. Therefore, in order to prevent the SO _{3 from} being sulfated in the AH to corrode the AH and prevent the solid content from adhering, the AH The exhaust gas temperature near the outlet must be kept above the acid dew point of SO ₃ (about 160 ° C.). For this reason, the exhaust gas temperature in the vicinity of the AH outlet cannot be reduced to about 160 ° C. or less, and as a result, the heat recovery efficiency of the AH is reduced, and the boiler efficiency is reduced.

[0004] Also, in the desulfurization apparatus, since the temperature of the exhaust gas inevitably drops below the acid dew point of SO _3, the SO ₃ in the exhaust gas, it is necessary to remove in EP desulfurizer upstream. Therefore, a large amount of NH ₃ or the like must be injected into the exhaust gas between AH and EP. In this case, unreacted ammonia gas is collected by the desulfurization device,
Since a large amount of the unreacted ammonia gas is contained in the desulfurization effluent, there is a problem that the wastewater treatment equipment becomes expensive.

Further, in the conventional flue gas treatment system, the conversion of SO ₂ to SO ₃ by oxidation is promoted in the De-NO _X on the upstream side of AH, and as a result, AH and EP
There is a problem that the SO ₃ concentration in the exhaust gas sent to the furnace further increases.

The inventor of the present invention has proposed that a part of reducing gas (CO, H ₂ S, HCN, etc.) generated between a burner in a boiler and an over-air port (hereinafter referred to as OAP) is transferred to the burner. withdrawn through the evacuation line provided between the OAP, by utilizing the gas in De-NO _X, together with reducing the amount of NH ₃ to be injected into the boiler in the exhaust gas, the SO ₃ concentration in the exhaust gas A method for reducing the noise has been proposed before (Japanese Patent Application No. 9-68052).

[0007]

However, in this method, since the gas temperature of the reducing gas extracted from the boiler is as high as about 1,500 to 1,600 ° C., the extraction line (particularly,
There is a problem that the material of the constituent material of the (introduction port) is limited, and it becomes very expensive. In addition, since the extracting position of the reducing gas is between the burner and the OAP, it is difficult to extract the reducing gas in a layout (technically) manner.

Accordingly, the present invention solves the above-mentioned problems, and reduces the amount of NH ₃ injected into boiler exhaust gas and reduces the SO ₃ concentration in the exhaust gas at low cost and easily. And a method and apparatus for reducing NOx concentration.

[0009]

The invention of claim 1 in order to achieve the above object, there is provided a means for solving] a high S, SO _X and NO of the boiler in the exhaust gas when the fuel containing V content is burned in a boiler
_{In the X} concentration reduction method, a gas for an ignition burner is injected into the vicinity of an exhaust gas inlet of a denitration device on the downstream side of the boiler.

According to the above method, the LPG gas used for the burner ignition is simply injected into the vicinity of the exhaust gas inlet of the denitration device, and it is not necessary to extract the high-temperature reducing gas. Compared with the conventional method, the amount of NH ₃ injected into the boiler exhaust gas can be easily reduced in terms of equipment and technology, and the SO ₃ concentration in the exhaust gas can be reduced.

[0011] According to a second aspect of the invention, a high S, SO _X in the boiler exhaust gas at the time of a fuel containing V content is burned in a boiler
And in the NO _x concentration reduction method, after extracting a part of the reducing gas generated in the boiler from the bottom of the boiler furnace,
The gas is injected into the vicinity of the exhaust gas inlet of the denitration device on the downstream side of the boiler via the extraction line.

According to a third aspect of the present invention, after a part of the reducing gas is withdrawn from the bottom of the boiler by suction, the gas is cooled, and the cooling gas is discharged through a withdrawal line to a denitration device on the downstream side of the boiler. a SO _X and NO _X concentration reduction method of the boiler flue gas according to claim 2 wherein the injection in the vicinity of the exhaust gas inlet.

According to the above method, since the reducing gas is extracted not from above the high-temperature boiler but from the bottom of the relatively low-temperature boiler furnace, it is easy to extract the reducing gas, and the reducing gas above the boiler can be easily removed. Since the reducing gas at the bottom of the boiler furnace, which has a relatively low temperature, is extracted, the degree of freedom in selecting the components of the extraction line is increased, and the cost of the apparatus can be reduced.

[0014] A fourth aspect of the present invention, a high S, SO _X in the boiler in the exhaust gas when the fuel containing V content is burned in a boiler
And the NO _X concentration reduction apparatus, the vicinity of the exhaust gas inlet connected denitration apparatus on the downstream side of the boiler, is provided with a gas injection means for igniting the burner.

According to the above configuration, since the gas injection means for the ignition burner utilizing a part of the existing equipment is provided near the exhaust gas inlet of the denitration apparatus, it can be applied to the existing flue gas treatment system as it is. be able to.

[0016]

Embodiments of the present invention will be described below.

SO _X and N in boiler exhaust gas of the present invention
A schematic diagram of O _X concentration reduction apparatus shown in FIG.

In a general flue gas treatment system, as shown in FIG. 1, a De-NO _X
2, AH3 and EP4 are connected.

SO _X and N in boiler exhaust gas of the present invention
O _X concentration reduction apparatus, in order to inject LPG gas G ₁ in the vicinity of the exhaust gas inlet of the De-NO _X 2, LPG gas injection means in the vicinity of the exhaust gas inlet of the De-NO _X 2 (gas injection means for ignition burner) 7 is provided.

The LPG gas injection means 7 is composed of an LPG gas supply 8 and an LPG gas injection line 9 connecting the LPG gas supply 8 and the vicinity of the exhaust gas inlet of De-NO _X 2. .

Here, a burner 5 for performing boiler combustion is provided.
Is composed of a main burner (not shown) and an ignition burner (not shown), and L is used as a fuel gas for the ignition burner.
PG gas G ₁ is being used. That is, the LPG gas supply unit 8 is provided as an auxiliary equipment of the burner 5 constituting the boiler 1.
Is originally placed, so a new LPG gas supply 8
It is not necessary to newly install the LPG gas injection line 9 only.

SO _X and N in boiler exhaust gas of the present invention
According to O _X concentration reduction apparatus, the existing LPG gas supplier 8
However, since only the LPG gas injection line 9 is newly provided, the present invention can be applied to an existing flue gas treatment system without updating the boiler 1 and the devices such as De-NO _X 2.

The temperature of the LPG gas G ₁ injected near the exhaust gas inlet of De-NO _X 2 is not as high as the reducing gas generated in the boiler 1. It is not necessary to use a special material as a constituent material, and the apparatus cost can be reduced.

Next, the method for reducing the concentration of SO _X and NO _{X in} the boiler exhaust gas of the present invention will be described with reference to FIG.

A fuel containing a large amount of S and V, such as orimulsion, is supplied and burned from the tip of a burner 5 provided in the boiler 1 to burn the boiler. At this time, in the burner 5, a NO _X mitigation performs combustion with less than the stoichiometric amount of air the air (incomplete combustion), then, downstream of the burner 5 (in FIG. 1 the upper) provided OAP6 And sufficient air is supplied to perform two-stage combustion to completely burn CO.

The boiler exhaust gas generated by the boiler combustion is discharged from the top of the boiler 1 and then passes through a gas mixer (not shown) so that the concentration distribution of each gas component in the exhaust gas becomes substantially uniform. , it is introduced into the De-NO _X 2.

In De-NO _X 2, an NO _X decomposition reaction represented by the following formula and a formula is carried out by the action of a denitration catalyst.

[0028] _{4NO + 4NH 3 + O 2 →} 4N 2 + 6H 2 O ... 2NO 2 + 4NH 3 + O 2 → 3N 2 + 6H 2 O ... In addition, in the exhaust gas during normal boiler operation hundreds ppm~ several thousand ppm of SO _There is abundant O ₂ (excess O ₂ ) of about ₁ to 3 wt% relative to ₂ . Therefore, in the oxidation reactor De-NO _X 2, the reaction from the left side to the right side in the equation shown in Chemical formula 1, that is, the conversion reaction to SO ₃ is promoted.

[0029]

Embedded image

For this reason, SO_ThreeThe conversion reaction to
In other words, promote the reaction from the right side to the left side in the expression
In order for O_TwoOther reducing components in excess of
SO _TwoInjection of a component having a higher oxidizing property is required.

In the present invention, as the reducing component,
LPG gas supply 8 near the exhaust gas inlet of De-NO _X 2
And LPG gas (C
₃ H ₈₎ implanting G _1.

In determining the injection amount of the LPG gas G ₁ , in addition to excess O ₂ in the boiler exhaust gas, SO ₃ ,
It is also necessary to consider the reaction such as NO _X,
Among these gas components, O ₂ , SO ₃ , NO _X , and NH ₃ , which are general as boiler exhaust gas components, are considered.
Moreover, those for NO _X, if the denitration rate is X, it is assumed that only the unreacted portion of 1-X contributes to reaction with LPG gas G _1, calculated on the effect of the NH ₃ is to be included in the denitration ratio X And Further, consider when calculating the injection amount of LPG gas G _1, the reaction of the formula - shown below (oxidation-reduction reaction in De-NO _X 2).

C ₃ H ₈ + SO ₂ + 5O ₂ → 3CO ₂ + 4H ₂ O + SO ₂ ... C ₃ H ₈ + 10SO ₃ → 3CO ₂ + 4H ₂ O + 10SO ₂ ... C ₃ H ₈ + 10NO → 3CO ₂ + 4H ₂ O + 5N ₂ . CmHn and HCN are not considered in the calculation because only a very small amount is contained in the boiler exhaust gas.

The concentration of each gas component is set to [C ₃ H ₈ ] wt%
(Weight% in exhaust gas), [O ₂ ] wt%, [SO ₃ ] p
pmw (weight ppm in exhaust gas) and [NO] ppmw, the exhaust gas amount is W (kg / h), and the C ₃ H ₈ injection amount is [C
Assuming that [ ₃ H ₈ ] (kg / h), the denitration rate is X, and the margin is 10%, the C ₃ H ₈ injection amount ([C ₃ H ₈ ] (kg / h))
Is represented by the formula of Chemical Formula 2.

[0035]

Embedded image

The reduction 2 C ₃ H ₈ calculated by (LPG gas G ₁₎ injection volume is the largest base, because actually deficiency occurs in each reaction, injecting the C ₃ H ₈ in the calculation amount , A considerable amount of unreacted C at the outlet of De-NO _X 2
It is believed that ₃ H ₈ is detected. Also, the boiler flue gas, CO also having reducing the LPG gas G _1, N
When H ₃ , CmHn, HCN, etc. are present, LPG
Injection amount of the gas G ₁ is the direction to decrease.

[0037] Thus, to inject LPG gas G ₁ in the vicinity of the exhaust gas inlet of the De-NO _X 2, the conversion reaction of the SO ₃ in the De-NO _X 2, it is suppressed as shown in equation At the same time, SO ₃ generated in the boiler 1 and contained in the boiler exhaust gas is decomposed into SO ₂ as shown by the equation.
As a result, the exhaust gas whose SO ₃ concentration has been significantly reduced becomes De-
It sent from NO _X 2 to AH3.

Further, as shown in the equation, the LPG gas G ₁ injected near the exhaust gas inlet of De-NO _X 2 has a strong reducing property, so that the LPG gas G ₁ in the above-mentioned NO _X decomposition reaction (see the equation and the equation) to serve as a replacement for NH _3, De-
The amount of NH ₃ injected into NO _X 2 can be reduced as compared with the conventional case.

That is, SO in the boiler exhaust gas of the present invention
According to the _X and NO _X concentration reduction method, the LPG used for burner ignition near the exhaust gas inlet of De-NO _X 2
Simply injecting gas G _1, reduce the amount of NH ₃ to be injected into the boiler flue gas, to suppress the conversion reaction to SO _3,
In addition, SO ₃ can be decomposed into SO ₂ , which is easier in terms of equipment and technology than conventional methods.

Further, since the exhaust gas temperature near the outlet of AH3 can be made much lower than in the past, the operating efficiency is improved and the amount of NH ₃ injected for collecting SO ₃ in EP4 is greatly increased. Can be reduced,
In addition, the size of the EP 4 itself can be reduced.

Next, another embodiment of the present invention will be described.

SO _{X in} Boiler Exhaust Gas of Another Embodiment
And shows a schematic diagram of the NO _X concentration reduction apparatus in FIG.

In the present embodiment, S in the boiler exhaust gas
Also in flue gas treating system using the O _X and NO _X concentration reduction apparatus, similar to FIG. 1, on the downstream side of the boiler 1, in _{order, De-NO X 2, AH3} , EP4 are connected.

The apparatus for reducing the concentration of SO _X and NO _{X in} boiler exhaust gas of the present embodiment injects a part of the reducing gas G ₂ generated in the boiler 1 near the exhaust gas inlet of De-NO _X 2. To this end, an extraction line 11 connecting the furnace bottom of the boiler 1 and the vicinity of the exhaust gas inlet of De-NO _X 2 is provided.

[0045] The middle of the extraction line 11, a suction fan 12 for extracting the reducing gas G _2, the gas cooler 13 for cooling the withdrawal reducing gas G ₂ is provided.

According to the apparatus for reducing the concentration of SO _X and NO _{X in} the boiler exhaust gas of the present embodiment, one end of the extraction line 11 for the reducing gas G ₂ is connected to the furnace bottom of the boiler 1, since the extracted relatively temperature is low boiler 1 hearth reducing gas G ₂ is more reducing gas extraction freedom of material selection of construction material line 11 is increased, it is possible to reduce the apparatus cost.

Next, S in the boiler exhaust gas of the present embodiment is
The method for reducing the concentration of O _X and NO _X will be described with reference to FIG.

The boiler exhaust gas produced by boiler combustion in the same manner as in the present invention is discharged from the top of the boiler 1 and then passes through a gas mixer (not shown) so that the concentration distribution of each gas component in the exhaust gas is reduced. It becomes almost uniform, and then De-NO _X
2 is introduced.

At this time, the burner 5 in the boiler 1 and the OAP 6
In the part between and CO, CO,
H ₂ S, a relatively large amount (several thousands ppm) is reducing gas G ₂ such as HCN is generated. A part of the reducing gas G ₂ generated in the boiler 1 is extracted from the furnace bottom of the boiler 1 through an extraction line 11 by a suction fan 12, and the extracted reducing gas G ₂ is removed from a gas cooler 13. Cool using. Thereafter, the cooled reducing gas G ₂ is injected into the vicinity of the exhaust gas inlet of De-NO _X 2 connected downstream of the boiler 1.

Here, heavy oil (for example,
Internal pressure of a boiler using
Since the pressure is higher than the atmospheric pressure, the reducing gas G ₂ is injected from the boiler 1 through the extraction line 11 into the vicinity of the exhaust gas inlet of De-NO _X 2 simply by suctioning with the suction fan 12. become.

Each reaction of the reducing gas G ₂ in De-NO _X 2 is shown by the following formulas.

CO (etc.) + SO ₂ + 1 / 2O ₂ → CO ₂ + SO ₂ ... CO + SO ₃ → CO ₂ + SO ₂ ... (Or 2HCN + 5SO ₃ → 2CO ₂ + N ₂ + H ₂ O + 5SO ₂ ) CO (etc.) + 10NO → CO ₂ + N ₂ ... As shown in the equation, the reducing gas G ₂ is more easily oxidized than SO ₂ contained in the boiler exhaust gas (it is oxidized before SO ₂ ). The indicated conversion reaction to SO ₃ (reaction from the right side to the left side) is suppressed. Therefore, the amount of SO ₃ produced by the reaction of the formula is reduced as compared with the conventional flue gas treatment system.

When the reducing gas G ₂ and O ₂ react quickly to reduce O ₂ , the reaction in the equation proceeds from right to left. As a result, SO ₃ generated in combustion in the boiler 1 and present in the boiler exhaust gas is decomposed into SO ₂ as shown in the equation, and the concentration of SO _{3 in} the exhaust gas further decreases.

[0054] At this time, the concentration of O ₂ in the De-NO _X 2 is too high, SO ₃ together with the reaction in the formula does not proceed from right to left is not decomposed into SO _2, conversely, from left to right Attention must be paid to the progress of the oxidation of SO ₂ to SO ₃ . On the other hand, when the concentration of O ₂ in the De-NO _X 2 is too low, the reducing gas G ₂ can not be sufficiently oxidized, De-NO
The conversion reaction of _X 2 to SO ₃ is not sufficiently suppressed. Therefore, in order to maintain the O ₂ concentration in the De-NO _X 2 within a range where the reducing gas G ₂ can be sufficiently oxidized and the conversion reaction to SO ₃ is not promoted, the O ₂ concentration to the extraction line 11 is reduced. Adjust the injection amount of air appropriately.

As described above, the reducing gas G ₂ extracted from the furnace bottom of the boiler 1 via the extraction line 11 is converted into De-NO _X
2, the conversion reaction of De-NO _X 2 into SO ₃ is suppressed as shown in the equation, and the SO 2 is generated in the boiler 1 and contained in the boiler exhaust gas. ₃ is decomposed into SO ₂ as shown in the equation. As a result, exhaust gas with significantly reduced SO ₃ concentration
It sent from the de-NO _X 2 to AH3.

Further, as shown in the equation, the reducing gas G ₂ injected near the exhaust gas inlet of De-NO _X 2 has the above-mentioned NO _X decomposition reaction (see equation and equation) because of its strong reducing property. To serve as a substitute for NH ₃ in De-
The amount of NH ₃ injected into NO _X 2 can be reduced as compared with the conventional case.

It should be noted that SO in the boiler exhaust gas of this embodiment is
It goes without saying that the same effect as that of the method of the present invention is also exerted in the x and NOx concentration reduction method.

[0058]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) By injecting an ignition burner gas used for burner ignition near the exhaust gas inlet of De-NO _X , the amount of NH ₃ injected into the boiler exhaust gas can be reduced and the exhaust gas can be reduced. The concentration of SO ₃ in the material can be reduced, which is easier in terms of equipment and technology as compared with the conventional method.

(2) By installing a new LPG gas injection line for the existing LPG gas supply, the boiler and
Without updating the device, such as a de-NO _X, it can be directly applied to the existing flue gas treatment system.

(3) One end of the reducing gas extraction line is connected to the bottom of the boiler, and the reducing gas at the bottom of the boiler whose temperature is relatively lower than the reducing gas above the boiler is extracted. The degree of freedom in selecting the material of the components of the extraction line is increased,
Equipment costs can be kept low.

[Brief description of the drawings]

FIG. 1 shows SOx and NOx in boiler exhaust gas of the present invention.
It is a schematic diagram of a concentration reduction device.

FIG. 2 is a schematic view of a device for reducing the concentration of SOx and NOx in boiler exhaust gas according to another embodiment.

[Description of Signs] 1 Boiler 2 De-NO _X (DeNOx device) 5 Burner 6 OAP (Over air port) 7 LPG gas injection means (Ignition burner gas injection means) 8 LPG gas supply device (Ignition burner gas injection means) 9 LPG gas injection line (gas injection means for ignition burner) 11 Extraction line 12 Suction fan 13 Gas cooler G ₁ LPG gas (ignition burner gas) G ₂ reducing gas

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F23J 15/00 B

Claims (4)

[Claims] In a method for reducing the concentration of SO _X and NO _{X in} boiler exhaust gas when a fuel containing high S and V content is burned in a boiler, the method includes the steps of: A method for reducing the concentration of SO _X and NO _X in boiler exhaust gas, wherein a gas for an ignition burner is injected. 2. A method for reducing the concentration of SO _X and NO _{X in} boiler exhaust gas when a fuel containing a high S and V content is burned in a boiler, wherein a part of the reducing gas generated in the boiler is removed by the boiler. after extracted from the furnace bottom, SO _X in the boiler flue gas, characterized by injecting the gas in the vicinity of the exhaust gas inlet of the denitration apparatus of the boiler downstream through the discharge line
And NO _X concentration reduction method. 3. After a part of the reducing gas is extracted from the bottom of the boiler furnace by suction, the gas is cooled, and the cooled gas is discharged through an extraction line in the vicinity of an exhaust gas inlet of a denitration device downstream of the boiler. 3. The method for reducing the concentration of SO _X and NO _{X in} boiler exhaust gas according to claim 2, wherein the SO _X and NO _X are injected into a boiler. 4. An apparatus for reducing the concentration of SO _X and NO _{X in} exhaust gas from a boiler when a fuel containing a high S and V content is burned in the boiler, the exhaust gas being introduced into a denitration device connected downstream of the boiler. An apparatus for reducing the concentration of SO _X and NO _X in boiler exhaust gas, wherein a gas injection means for an ignition burner is provided near the mouth.